1. Field of the Invention
The invention relates to a medical implantable lead of the type adapted to be inserted into a human or animal body and attached to an organ inside the body for monitoring and/or controlling the function of the organ, and having a header in a distal end, a fixation means and an electrode arranged in the header, wherein the fixation means attaches the distal end of the lead to the organ and the electrode is arranged to transmit or receive electrical signals to or from the organ, a connector in a proximal end that includes a connector pin and is adapted to be connected to a monitoring and/or controlling device, and an inner coil, which extends inside an outer casing of the lead and is adapted to transmit electrical signals between the monitoring and/or controlling device and the electrode, wherein the inner coil is attached to the connector pin.
The invention also relates to method for manufacturing of a medical implantable lead of the above type.
2. Description of the Prior Art
Medical implantable leads of the above type are commonly used for example for monitoring and/or controlling the function of a human or animal heart. In such a case a proximal end of the lead is connected to a monitoring and/or controlling device such as a pacemaker or a cardiac defibrillator, whereas a distal end of the lead is inserted into the body and attached to the heart by means of some kind of fixation means. The distal end of the lead comprises at least one electrode, which is in electrical contact with the proximal end by means of an inner coil of helically formed metal wires inside the lead. The fixation means can be of a type having projections, such as fins or tines, which will engage in the trabecular network inside the heart. The fixation means can also be a penetration member, such as a barbed needle or as a helix which is screwed into the tissue of the heart, either as a helix which is unrotatable in relation to the lead, in which case the entire lead is rotated when attaching the helix, or a rotatable helix which can be rotated in relation to the lead from the proximal end by means of the inner coil, which is rotatably arranged inside the lead. A rotatable helix can be rotatable but non-extendable in relation to the lead, or it can be rotatable and extendable, in which case the helix is accommodated inside a sleeve formed header in the distal end of the lead and will be screwed out from the header when attaching it to the tissue. In the latter case the inner coil will accordingly be stretched out when attaching the helix to the tissue. The penetration member can also function as an electrode inside the tissue, in which case the penetration member is electrically connected to the inner coil, or be separated from the electrode, in which case the penetration member is not electrically connected to the inner coil.
In the proximal end the inner coil is connected, mechanically as well as electrically, to a connector pin, which can be electrically connected to a monitoring and/or controlling device and which is accommodated in a connector housing. In case the lead comprises a rotatable helix in the distal end, the connector pin is rotatably journaled inside the connector housing.
As is evident from the above description, the inner coil will have several functions. Firstly, it will function as an electrical conductor for transferring of electrical signals between the monitoring and/or controlling device and the electrode in the distal end. In case the lead comprises a rotatable helix in the distal end, the inner coil shall also transfer rotary motion from the proximal to the distal end. In case the rotatable helix also is extendable, the inner coil will also be elongated to maintain the mechanical as well as electrical contact with the helix during rotation and advancement. Furthermore, the inner coil shall contribute to the desired bending characteristics of the lead, i.e. the lead has to be flexible but should have sufficient stiffness to be insertable through a vein or the like. Finally, the inner coil will define an inner lumen in the lead, into which a guide wire or stylet may be inserted during implantation, for guiding the distal end of the lead to a suitably position abutting with its distal end against an organ inside the body and subsequent fixation by the fixation means, e.g. by screwing in of the helix into the organ.
In the prior art, the inner wire coil is attached to the connector pin at a distal end portion of the connector pin. For example can the inner coil be welded to the connector pin or be attached by means of a clamp connection, in which case a proximal portion of the inner wire coil often is thread onto a support tube to prevent collapsing of the coil section during clamping, and the support tube as well as the thread up portion of the inner coil is inserted into a bore from the distal end of the connector pin and fixated therein by clamping and deforming of the connector pin. Accordingly, the connector pin in prior art is normally provided with an enlarged bore in a distal portion to allow insertion and attachment of the inner coil inside the connector pin. A proximal portion of the connector pin, on the other hand, is only provided with a small diameter bore to allow insertion of a guide wire or the like when implanting the lead into the body.
However, there are several disadvantages associated with attaching the inner coil with the connector pin in the distal end. For one thing, this operation is complex to perform since the available space to perform the attachment is very limited. Moreover, the inner coil has to be pre-cut in correct length before assembling, wherein the length can not be altered afterwards, and this is critical since e.g. the performance of a rotatable and extendable fixation helix depends in high degree on the length of the inner coil. This is due to the fact that the inner coil in practice functions as a helical spring and tensile stress will arise in the inner coil if the length is to short, since then it has to be stretched when attaching to the connector pin, with the potential risk that the helix will tend to rotate after attaching to the organ which can cause disengagement of the lead from the organ. When such an incorrect length of the inner coil is detected after assembling but before use, the entire lead has to be discarded. Moreover, when the inner coil is attached to the connector pin, this can cause the coil windings to become uneven and wave shaped, which will increase the friction against an inner tubing, which encloses the inner coil and in relation to which the inner coil is rotatable. A medical implantable lead constructed in this way also has to be assembled by one component at a time from one of the ends of the lead. This has to effect that if one of all the components forming the medical implantable lead should fail or be incorrect mounted, the entire medical implantable lead has to be discarded.
The aggregate dimensional tolerances of the component parts as well as the assembling tolerances will affect the actual required length of the inner coil and hence it is difficult to estimate the nominal cut length of the inner coil in advance. This necessitates close dimensional as well as assembling tolerances, in order to limit the number of discards, and this increases the manufacturing costs for the medical implantable lead.